FIG. 1, numeral 100 shows a conventional edge emitting laser diode 10 that is attached to a carrier 12 which is mounted on a substrate 14. A photo sensor 16 is generally placed under the rear surface/rear mirror 18 of the edge emitting laser diode 10. In most systems utilizing semiconductor lasers, dynamic stabilization and control of the optical output power is required. In edge emitting laser diodes this is usually accomplished by allowing a portion of the light 20 emitted by the laser diode, i.e., using light emitted from the laser diode's rear mirror 18 for bias control, to illuminate the photo sensor 16 which produces a photocurrent proportional to the intensity of a beam of light 22 emitted by the edge emitting laser diode 10. This optically generated photocurrent, in turn drives a feedback circuit which controls the laser bias current. In contrast, however, in an optical package utilizing a Vertical Cavity Surface Emitting Laser (VCSEL), light emitted from the rear mirror is absorbed by the GaAs substrate used in the VCSEL. Thus, the system of using light emitted from the rear mirror is unavailable for bias control in VCSEL structure.
A VCSEL is a semiconductor laser diode in which the laser oscillation and the optical emission occur in a direction normal to the pn junction plane. The VCSEL has many properties which are advantageous when compared to the more commonly used edge-emitting laser diodes. These properties include: low optical beam divergence, a circular optical output, and single longitudinal mode operation. In addition, VCSEL devices are manufactured in a manner which allows wafer level testing of individual devices. These properties make VCSELs attractive in applications such as optical data storage, data communication and laser scanners.
Presently, in a VCSEL structure, a portion of the light beam emitted from the front surface of the laser is redirected by a single reflective surface onto a photo-sensing unit for automatic power control. Although, this arrangement provides satisfactory performance under most operating circumstances, however, the automatic power control operation may be affected by a variety of environmental conditions such as temperature variations.
Thus, there is a need for an optical package with automatic power control wherein the effects of temperature variations thereon are minimized.